1) Which one when spilt onto skin will cause the least damage
2) Which one is the safest to store
3) Which one is least likely to affect a person in long term
4) Which one would you rather have a kid handle ?
5) Overall, which one is the most safe to use?

1. Probably the ammonium perchlorate.
2. No idea.
3. Limit exposure - not really an issue. Pour, etch, pour back in container.
4. None of them. Under any circumstances (thinking 4 year old grandson).
5. I would choose FeCl. You can see it easily, and so clean it up. Despite the horrible stains, it doesn't fume.

1) Which one when spilt onto skin will cause the least damage
2) Which one is the safest to store
3) Which one is least likely to affect a person in long term
4) Which one would you rather have a kid handle ?
5) Overall, which one is the most safe to use?

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I have not used ammonium perchlorate. I have used ferric chloride, cupric chloride, HCl +H2O2, and H2SO4 + H2O2.

1) Ferric chloride causes staining, but not much more. Ammonium perchlorate is also pretty safe. The others (persulfate, cupric chloride, or HCl +H2O2)) have fairly high HCl or H2SO4 concentrations. H2SO4 is non-volatile, so if splashed, it stays on a surface until washed off or neutralized.

2) If you are concerned about build up of gas pressure, any etchant with "per" in its name and water can evolve a gas. Ferric chloride and cupric chloride are very stable; the others as solutions can loose effectiveness on storage, but that activity can be regenerated (in fact that is part of the process) by adding hydrogen peroxide. I am not sure of the stability of ammonium perchlorate. Presumably, it could lose some ammonia, and it would not be regenerated by adding hydrogen peroxide. For simple, long term storage, without loss of activity, it is hard to beat ferric chloride.

3) Long-term effects on people, don't know exactly. Remember, ferric chloride can be used as a food supplement, but usually ferric gluconate or some other salt is use to be gentle on your stomach. Cupric chloride is probably the most toxic if ingested, because of the copper. But, any etchant after use will contain copper.

4) None of them. As a kid, I used ferric chloride. Since it doesn't bubble, the risk of splashing is reduced. I would avoid those etchants prepared with relatively concentrated acids, namely HCl or sulfuric acid, and those requiring heat.

5) I prefer ferric chloride or cupric chloride. Neither bubbles, and I am careful not to drink them. Of the two, I would give the node to ferric chloride as being less toxic in small amounts. I have not used ammonium perchlorate, so I don't know if it bubbles.

Oh, to stop any worries, i only said the kid thing because...well...its hard to explain. IF a kid WAS to have some which one would it be,

I have a young brother, 11. He is very responsible and if you tell him to not touch something he WONT! But for some weird reason he "did" get it (even though im going to seal it in a plastic container inside a metal safe) which one would you rather him have. its complicated

Actually FeCl does fume, but not the way you mean. I've left tools in a box that had half a bottle that had been tightly sealed, the tools were ruined (from fumes).

The solution to the problem was simple enough though, I rolled a single square of paper towel around the lid tightly, and taped it into place. No fumes. When I pulled the tape off both the tape and paper in the paper towel had gone brittle, crumbling to dust as I worked with it. Again, no big deal, paper towels and tape are cheap.

I've handle FeCl with no problem, it does stain the skin and clothes, but it isn't harmful as far as I know.

1. Probably the ammonium perchlorate.
2. No idea.
3. Limit exposure - not really an issue. Pour, etch, pour back in container.
4. None of them. Under any circumstances (thinking 4 year old grandson).
5. I would choose FeCl. You can see it easily, and so clean it up. Despite the horrible stains, it doesn't fume.

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Ammonium perchlorate would not be an appropriate chemical for etching copper; you must be thinking of ammonium persulfate.